The present invention relates to a hybrid magnetic bubble memory device in which magnetic bubble propagation tracks formed of an ion-implanted layer and magnetic bubble propagation tracks formed of a soft magnetic material film (for example, a nickel-iron alloy film such as permalloy film) are both provided on a single chip including a magnetic medium for supporting a magnetic bubble, and more particularly to the junctions of the two magnetic bubble propagation tracks.
The hybrid magnetic bubble memory device was disclosed in a Japanese Patent Application Laid-Open No. 40971/1982, laid-open on May 6, 1982, the application filed in the name of Fujitsu, Ltd. and a U.S. application Ser. No. 375,344 (a U.S. Pat. No. 4,528,645 filed on May 5, 1982 (Priority date May 11, 1981)), the application filed in the name of Hitachi, Ltd. In the hybrid magnetic bubble memory device, ion-implanted tracks are used in data storage area for increasing the bit density and soft magnetic material tracks are used in functional parts such as generators, replicate gates, swap gates, read major lines and write major lines for stable function operations. The hybrid architecture is applicable to magnetic bubble memory devices of which bubble diameter is larger than 0.6 .mu.m where soft magnetic material tracks have good bubble propagation characteristics. The architecture realizes 4.about.16 Mb/cm.sup.2 magnetic bubble memory devices having good read/write functional characteristics.
In the hybrid magnetic bubble memory devices, ion-implanted tracks are superposed on soft magnetic material tracks in minor loops to form junctions where bubbles propagate from ion-implanted tracks to soft magnetic material tracks and from soft magnetic material tracks to ion-implanted tracks. Conventional junction designs are shown in FIGS. 2 and 3. Bubble propagation tracks near the replicate gate corner in minor loops are shown in FIG. 2. Ion-implanted tracks 2 are formed at the boundary of ion-imp.lantation region 1 and non-implantation region.
In the following description and the foregoing, non-ion-implanted region means the region in which ion-implantation to form ion-implanted tracks is not effected. Ion-implantation mask is used to form the non-ion-implanted region on ion-implantation process. Such ions are H.sub.2.sup.+, He.sup.+ and Ne.sup.+ are implanted all the surface of the memory device to suppress the generation of hard bubbles. In the non-ion-implanted region, ions for hard bubble suppression are implanted. Bubbles are propagated along the upper direction 3 on the ion-implanted tracks 2 and transferred to the soft magnetic pattern 4, and propagated along the soft magnetic patterns in the direction 3. A soft magnetic pattern 5 and a conductor pattern 6 form a replicate gate.
The replicate gate has a function to divide a bubble into two bubbles by pulsed current drive of the conductor pattern 6.
After the corner pattern 5 propagation, bubbles are propagated along the direction 7 to reach the other junction 8 where ion-implanted tracks 9 are superposed with a soft magnetic pattern 8.
At the junction 21, bubbles are propagated from soft magnetic tracks to ion-implanted tracks.
After all, the soft magnetic pattern 4 and ion-implanted track 2 form the type I junction 20 in which bubbles are propagated from the ion-implanted tracks to the soft magnetic tracks. The soft magnetic pattern 8 and ion-implanted track 9 form the type II junction 21 in which bubbles are propagated from the soft magnetic tracks to ion-implanted tracks.
Bubble propagation tracks near the swap gate corner in the minor loop is shown in FIG. 3. The type I junction and the type II junction are arranged in the reverse direction. Bubbles are propagated on the ion-implanted tracks 2 in the direction 10 and are transferred to the soft magnetic pattern 4 at the type I junction 20. Tnen propagated along the soft magnetic track to reach the swap gate corner pattern 12. The conductor pattern 13, the corner pattern 12 and other several soft magnetic patterns 18, 22, 24, 25 and 26 form the swap gate. Pulsed current drive of the conductor pattern 13 control the bubble in the minor loop to propagate along the direction 14 to the write major line 19. At the same time, the bubble on the write major line propagates along the direction 15 to the minor loop.
Bubbles, which propagate on the swap gate corner pattern 12 or which are transferred from the write major line 19 to the minor loop, then propagate on the soft magnetic patterns such as 16, in the direction 17 and reach the soft magnetic pattern 8 which is a component of the type II junction 21. On the soft magnetic pattern 8, bubbles are transferred from the soft magnetic track to the ion-implanted track 9. The period of the ion-implanted tracks in the minor loop as shown in FIG. 2 and FIG. 3 is 3 to 4 times of the bubble diameter. The period of the soft magnetic patterns which form the junctions, corner patterns and soft magnetic propagation patterns, is 10 to 20 times of the bubble diameter. Such large period patterns are used to increase drive force caused by rotating field Hr. of the small diameter bubbles which have large saturation induction Ms. Magnetization of the soft magnetic patterns due to the large bubble stray field which value is linear to Ms value. The smaller the bubble diameter, the larger the Ms value, which means the neccessity of large amplitude rotating field to drive small diameter bubbles. The increased period of the soft magnetic pattern enables the enlargement of bubble drive force, which results bubble propagation by low amplitude drive field. Minor loop length is enlarged by using 10 to 20 soft magnetic pattern having such a large period. The bit density of the magnetic bubble memory using ion-implanted tracks is reduced by using such enlarged soft magnetic patterns. Therefore, high density magnetic bubble memory device is realized by reducing the number of soft magnetic patterns having the enlarged period.
Another problem of the conventional hybrid magnetic bubble memory device is that the bubble drive force of the soft magnetic patterns is not large enough to propagate bubbles across the ion-implantation edges at the junctions for the lower drive field.
Therefore, the period of the soft magnetic pattern in the junction portion is set larger than that of the soft magnetic pattern in another portion.
For the drive field larger than 60 Oe, bias margin width of the junction is larger than 10% of the operating bias field.
The value decreases as the drive field becomes smaller. For the 50 Oe drive field, the bias margin is smaller than 7.about.8% of the operating bias field.
The increase of the soft magnetic pattern period enables the increase of the bubble drive force, and the upper end of the bias margin is higher. As though, too much enlargement of the soft magnetic patterns induces the bubble propagation errors at lower bias field edge.
The attractive pole generated by the drive field on the large period soft magnetic patturn has larger area than that on the small period soft magnetic pattern.
Therefore, bubbles on the large period soft magnetic pattern strech to be strip domains at higher bias field than those on the small period soft magnetic pattern.
The lower end of the bias margin becomes higher as the soft magnetic pattern period is larger.
Therefore, period increase of the soft magnetic patterns in the junctions is not the solution to improve the bubble propagation characteristics of the junctions.